The invention relates to a catalyst, in particular for reducing NO.sub.x, as well as to a method of reducing NO.sub.x.
Numerous methods of converting NO.sub.x into nitrogen are known.
For example, U.S. Pat. No. 5,149,512 describes a method of reducing NO.sub.x using methane, in the presence of oxygen, in which a catalyst consisting of a zeolite in particular of mordenite structure with a pore size of between 5 and 15 .ANG., exchanged with cobalt, is used.
However, the rate of conversion of NO.sub.x into nitrogen is very poor, that is to say in the neighbourhood of 27% at 450.degree. C. Moreover, this catalyst is exchanged with high percentages of cobalt, more specifically with 5.5% by weight of cobalt in relation to the total weight of the catalyst.
Moreover, European patent application No. EP-A-0 286 507 describes the use of a zeolite of mordenite structure in ammonium or acid form with socalled "large pores", that is to say with a pore size greater than 6.6 .ANG., for the reduction of NO.sub.x in the presence of oxygen. This document also describes the use of a zeolite of mordenite structure with socalled "small pores", that is to say with a pore size of less than 4.4 .ANG., exchanged with copper for the reduction of NO.sub.x in the presence of oxygen. However, in the latter case, ammonia is used as NO.sub.x reducing agent. In fact, the use and the storage of ammonia are very difficult. Moreover, no mention was made in this document of the activity of these catalysts in terms of percentage of conversion of NO.sub.x.